Storage library systems are often used by enterprises and the like to efficiently store and retrieve data from storage media. In the case of some storage libraries, the media are data cartridges (e.g., tape cartridges) that are typically stored and indexed within a set of magazines. When particular data is requested, a specialized robotic mechanism finds the appropriate cartridge, removes the cartridge from its magazine, and carries the cartridge to a drive that is designed to receive the cartridge and read its contents. Some storage libraries have multiple drives that can operate concurrently to perform input/output (I/O) operations on multiple cartridges.
One limitation of some such storage library systems is that the throughput of the system (e.g., how quickly data can be accessed) is at least partly dependent on physical constraints relating to moving the robot, picking and placing cartridges, etc. For example, expanding the size of the library can effectively increase the distances traversed by the robot when performing pick and place operations, and the like, which can thereby increase access times and reduce throughput. Another limitation of some such storage library systems is that a fixed number of cartridges fit in the library. For example, if a library is intended to fit in half of a standard equipment rack, that overall footprint can drive the space available for cartridges, magazines, etc. To use more cartridges, customers typically purchase an additional library that operates independent of the other library.